The present invention relates to a photographic printer, and more particularly to a printer for providing appropriate control of a light source for illuminating photographic film.
A photographic printer is provided with a printing light source such as a halogen lamp, which illuminates negative film to print picture frames on color paper. The halogen lamp in the printer changes with time, and accordingly is conditioned to compensate for gradual change. In a printer for use in a mini laboratory (printer-processor), a scanner is incorporated for automatically discriminating a type of scene recorded on a picture frame in order to prevent a subject failure. A color image area sensor or a monochrome image area sensor is used for the scanner, which subjects each point of the picture frame to three color separation photometry, calculates various characteristic values, and discriminates a scene to be printed so as to obtain such correction values for calculating an optimum exposure amount as a color correction coefficient. This scanner is used not only for photometry to obtain the exposure amount, but also for detecting a position taken by the picture frame from the surface of the negative film in order to position each picture frame in the exposure station.
To condition the light source, the power is adjusted to correct the gradually changed light source. Specifically, normal control negative film (Bull's eye) formed primarily of a widespread type of negative film, such as FUJI HR 100 (merchandise name) is positioned on a film carrier, and is subjected to photometry to obtain a density (a large area transmittance value or a transmittance value of a particular partial area), which is compared with that of the same normal control negative film measured before the change of the light source. The difference in density is used to correct the light source. However, there is a problem of complexity in the light source conditioning, because the normal control negative film fades with time, and must be conditioned. There is also a problem in that an operator incorrectly may use over-exposed control negative film and under-exposed control negative film for the light source conditioning, which are prepared for determining various other conditions.
In a photographic printer which employs additive color successive exposure, three additive primary color filters are used as exposure filters. A monochrome image area sensor is used as the scanner in combination with the color filters. Because the light amount is excessive for the image area sensor when it is used as the scanner, especially with respect to blue light, the amount of the blue light is reduced by an ND filter. However, this construction causes a problem in that parts and operations necessary to assemble the parts are increased, because an ND filter must be set in front of a blue filter on the filter turret or on the light receiving plane of the sensor.
To detect a picture frame on the film with the scanner, the white light illuminating the negative film without restricting the light amount causes such saturation of the image area sensor as to make photometry impossible, because the light amount is excessive. Thus, an ND filter is provided to restrict a light amount incident on the image area sensor in the picture frame detecting procedure. There is a similar problem in the greater number of parts and operations.
Therefore, it is an object of the present invention to provide a photographic printer that is easily capable of performing photometry to detect a position of a picture frame and calculating an exposure amount, even without an ND filter.
It is another object of the present invention to provide a photographic printer capable of conditioning the light source reliably without operational error.